Conventionally, communication systems have been adapted to send and receive information using a radiation field (radio waves), for example, between mobile telephones, and send and receive information via electromagnetic induction, for example, between the coil in a data reader/writer provided on a ticket checking and, collecting machine at a station and the coil in an IC card.
Recently, there have been proposed communication systems which are provided with a human-body-side communication device fitted in contact with the skin of a human body and an equipment-side communication device in the neighborhood of the user. In these communication systems, an alternating voltage is applied to the human body via the electrode of the human-body-side communication device, and as a result, there is caused an electrostatic induction phenomenon at the electrode of the equipment-side communication device by the action of a capacitor using a human body intervening between the electrodes of the communication device on the human body side and the communication device on the equipment side as a medium. Using the electrostatic induction phenomenon, information is sent and received (see Non-patent document 1, for example).
In addition to these communication systems, there have been proposed a lot of communication systems adapted to send and receive information utilizing the electrostatic induction phenomenon caused at a receiving electrode by the action of a capacitor using a human body intervening between sending and receiving electrodes as a medium (see Patent documents 1 to 9 and Non-patent documents 2 to 5).
[Patent document 1] National Publication of International Patent Application No. 11-509380
[Patent document 2] U.S. Pat. No. 3,074,644
[Patent document 3] Japanese Patent Laid-Open No. 10-228524
[Patent document 4] Japanese Patent Laid-Open No. 10-229357
[Patent document 5] Japanese Patent Laid-Open No. 2001-308803
[Patent document 6] Japanese Patent Laid-Open No. 2000-224083
[Patent document 7] Japanese Patent Laid-Open No. 2001-223649
[Patent document 8] Japanese Patent Laid-Open No. 2001-308803
[Patent document 9] Japanese Patent Laid-Open No. 2002-9710
[Non-patent document 1] Internet <URL:http://www.mew.co.jp/press/0103/0103-7.htm>(retrieved on Jan. 20, 2003)
[Non-patent document 2] “Development of Information Communication Device with Human Body Used as Transmission Line” by Keisuke Hachisuka, Anri Nakata, Kenji Shiba, Ken Sasaki, Hiroshi Hosaka and Kiyoshi Itao (Tokyo University); Mar. 1, 2002 (Collected Papers for Academic Lectures on Micromechatronics, Vol., 2002, Spring, pp. 27-28)
[Non-patent document 3] “Development of Communication System within Organism” by Anri Nakata; Keisuke Hachisuka, Kenji Shiba, Ken Sasaki, Hiroshi Hosaka and Kiyoshi Itao (Tokyo University); 2002 (Collected Papers for Academic Lectures for Japan Society of Precision Engineering Conference, Spring, p. 640)
[Non-patent document 4] “Review on Modeling of Communication System Utilizing Human Body as Transmission Line” by Katsuyuki Fujii (Chiba University), Koichi Date (Chiba University), Shigeru Tajima (Sony Computer Science Laboratories, Inc.); Mar. 1, 2002 (Technical Reports by The Institute of Image Information and Television Engineers Vol. 26, No. 20, pp. 13-18)
[Non-patent document 5] “Development of Information Communication Device with Human Body Used as Transmission Line” by Keisuke Hachisuka, Anri Nakata, Kento Takeda, Ken Sasaki, Hiroshi Hosaka, Kiyoshi Itao (Graduate School of Science of New Region Creation, Tokyo University) and Kenji Shiba (Science and Engineering Course, Tokyo University of Science); Mar. 18, 2002 (Micromechatronics Vol. 46; No. 2; pp. 53-64)
In these communication systems with such a configuration, since the action of a capacitor using a human body intervening between sending and receiving electrodes as a medium is the premise of physical action, the communication strength in communication between the electrodes depends on the area of the electrodes.
Furthermore, since the action of a capacitor using a human body intervening between sending and receiving electrodes as a medium is the premise of physical action, it is physically impossible, when the sending electrode is fitted to the human's right wrist, for example, to communicate in directions other than the direction from the human's right wrist to the fingertip. When the sending electrode is fitted near the human's chest, communication in directions other than the forward direction from the human's chest is physically impossible.
As described above, in communication systems, since the action of a capacitor using a human body intervening between sending and receiving electrodes as a medium is the premise of physical action, there have been a problem that the communication direction is restricted by the position of the electrode fitted to a human body-as well as a problem that the degree of freedom in communication is low because the communication strength depends on the electrode area.